Pursuant to 35 U.S.C. §103(c)(2), the claimed invention was made by an employee of a party to a joint research agreement and as a result of activities undertaken within the scope of the joint research agreement. The parties to the joint research agreement were Virginia Polytechnic Institute & State University and the United States Air Force (U.S. Government).
Methods of modulating the magnetic field in micron-sized magnetic sensors have been disclosed for example in U.S. Pat. No. 6,501,268. U.S. Pat. No. 7,898,247 discloses a method based on using a rotating disc containing flux concentrators and guides which can be used with a larger sensor, but the motion of the rotating disk generates considerable acoustic noise. Fluxgate magnetometers operate using a similar principle to the one described here in that they drive magnetic material (in the case of a fluxgate a magnetic core) into and out of saturation.
Magnetoelectric magnet field sensors are disclosed in U.S. Pat. No. 7,023,206 to Viehland, et al., (hereinafter Viehland '206) issued Apr. 4, 2006, entitled “Magnetoelectric Magnetic Field Sensor with Longitudinally Biased Magnetostrictive Layer,” hereby incorporated by reference. Viehland '206 discloses a magnetoelectric magnetic field sensor having one or more laminated magnetostrictive layers and piezoelectric layers. The magnetostrictive layers are magnetized by a bias magnetic field in a longitudinal, in-plane direction. The piezoelectric layers can be poled in the longitudinal direction or perpendicular direction. For example, an L-P configuration represents a longitudinal MS magnetization combined with perpendicular PZ poling. Perpendicular poling of the piezoelectric layers tends to provide higher sensitivity at lower detection frequency (e.g. less than 1 Hz). Longitudinal poling tends to provide higher sensitivity at high detection frequency (e.g. above 10 Hz). Also disclosed in Viehland '206 are embodiments having relative thicknesses for the magnetostrictive layers that are optimized for sensitivity. Further examples of a magnetoelectric sensor are disclosed in U.S. Pat. No. 7,771,846 to Veihland, et al., (Viehland '846) hereby incorporated by reference. Viehland '846 discloses a magnetoelectric composite laminate of at least one (1-3) piezo-fiber layer coupled with high-permeability alloy magnetostrictive layers formed of FeBSiC or equivalent. The composite laminate alternates the (1-3) piezo-fiber and high-permeability alloy magnetostrictive layers in a stacked manner with the magnetization direction of the high-permeability alloy magnetostrictive layers and polarization direction of the piezo-fiber layer being in an longitudinal-longitudinal (L-L) arrangement. Optionally, thin film polymer layers are between the (1-3) piezo-fiber layer and high-permeability alloy magnetostrictive layers. Optionally, piezo-electric fibers within the (1-3) piezo-fiber layer are poled by inter-digitated electrodes supported by the thin film polymer, arranged as alternating symmetric longitudinally-poled “push-pull” units.
There is a need for better performance of sensors, such as for example magnetoelectric magnetic field sensors, at low frequencies to detect weapons systems, vehicles, and, in general, ferromagnetic objects. Also, there is a need for improved magnetic sensors that can be use for controlling manufacturing processes, checking that the hearts of unborn babies for proper functioning, and, if nanomagnets are included as part of a drug, monitoring drug circulation through the bodies of patients.